Methods for the graphical representation of genomic sequence data

ABSTRACT

This disclosure provides a computational framework with related methods and systems to enhance the analysis of genomic information. More specifically, the disclosure provides for a graph-based reference genome framework, referred to as a GNOmics Graph Model (GGM), which represents genomic sequence information in edges with nodes representing transitions between edges. The disclosed GGM framework can represent all known polymorphisms simultaneously, including, SNPs, indels, and various rearrangements, in a data-efficient manner. The edges can contain weights to reflect the likelihood of a path within the GGM incorporating any particular edge. The disclosure also provides for systems and methods for using the GGM as a reference model for the rapid assembly of short sequence reads and analysis of DNA sequence variation with enhanced computational efficiency.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/161,147, filed May 20, 2016, which claims the benefit of U.S.Provisional Patent Application No. 62/165,543, filed May 22, 2015, whichare incorporated herein by reference in their entirety.

STATEMENT REGARDING SEQUENCE LISTING

The sequence listing associated with this application is provided intext format in lieu of a paper copy and is hereby incorporated byreference into the specification. The name of the text file containingthe sequence listing is 56389_Seq_Final_2016-05-20.txt. The text file is3.41 KB; was created on May 20, 2016; and is being submitted via EFS-Webwith the filing of the specification.

FIELD OF THE INVENTION

This disclosure provides methods and systems for a computationalframework to enhance the analysis of genomic information. Morespecifically, the disclosure provides graph-based reference genome, andmethods and systems for generating and using the reference genome, thatallow for the rapid assembly of sequence reads and determination of DNAsequence differences.

BACKGROUND

New advances in human DNA sequencing and computing technology are comingtogether to allow rapid identification of the complete genomes ofindividuals with striking potential for transforming personalizedmedicine. At present, key limitations to realizing the full potential ofwhole genome sequencing (WGS) include the time, expense, and reliabilityof processing DNA sequence data to generate the list of all variationspresent in an individual and to reveal those alterations that causedisease or modify the risk of disease. Advances in the analysis ofgenome sequences are, thus, critical for diagnosis and potentiallyinformative for treatment. Accordingly, bioinformatics and innovation incomputational methods are key drivers for improving the analysis andinterpretation of DNA sequence data.

The current price of WGS is approaching $1,000 for the laboratoryprocedures, but the time and expense of computational analyses andgenetic interpretation remains significantly higher. Currently, the mostwidely used approaches report the set of differences between anindividual and a global reference genome sequence, as most of the 3billion positions are the same. To obtain the set of differences, themost widely used computational approaches are based on a two-stepprocess: (1) read mapping and (2) variant calling. The data produced inWGS is a collection of millions of short (e.g., ˜150 letter) “reads”,where each letter is one of the four canonical DNA nucleotides (A, C, Gor T). These “reads” are then placed onto (“aligned against”) areference genome sequence in a manner akin to placing puzzle pieces ontoa picture of the puzzle. Read mapping algorithms take a single read andscan through a reference genome to find where the read fits best. Foreach read there are billions of possible positions to be considered.Once all reads have been placed, there are usually redundant overlappingreads (on average 30-100 copies per position). An algorithm is thenapplied to pass over the 3 billion characters of the reference genomeand evaluate statistically whether the mapped read data indicates acomplete match to the reference genome at each position, or if there isevidence that the individual being sequenced differs from the referenceeither partially or completely.

However, the mapping of reads remains a significant challenge. Most ofthe single nucleotide variations from the reference genome present inany individual are polymorphic, meaning that many other individuals havethe same sequence variation. It is estimated that roughly 85% of thevariants found in each individual are polymorphic and 15% are rarevariants. This variation can complicate alignment to the reference whensequence differences from the reference exist, potentially resulting ina failure to place the observed DNA sequence at the correct location.This reflects an allele bias in the reference. Reads that perfectlymatch the reference will be handled better than those that do not. Thus,the reference allele bias is a key source for errors in variantdetection associated with the widely used practice of WGS analysis. Thecurrent approaches to this analysis is to select a reference sequencethat is as similar to the new sequence as possible, and multipleapproaches of this kind have been introduced (for example, using anethnically similar reference genome for mapping). Such approaches arefundamentally oriented to using a reference which accounts for thecommon variants that are observed in a population. As a result,large-scale efforts are underway to provide a comprehensive inventory ofhuman genetic variation, and to identify rare variants causal forgenetic disorders and contributory to diverse diseases including forexample, the dbSNP database, the HapMap project, and the 1000 Genomesproject. In addition to these efforts, the recognition of the referenceallele bias has also motivated efforts to develop alternativecomputational approaches to represent a reference genome that canefficiently include these known polymorphic locations and, therefore,allow improved read mapping. Such an approach would allow read mappingsoftware to consider all recurring variations at each position, therebyeliminating or reducing the reference allele bias.

Another drawback to the existing alignment strategies is that theavailable reference genomes do not account for the existing variationthat may be relevant for the comparison. For example, there is currentlya global human reference genome (GRCh38) that is based on the combinedgenetic material of 13 anonymous individuals. A key limitation of theprimary human reference genome is that it is but a single reference anddoes not account for known variations. For instance, if 51% of sourcepeople have an A at position X and 49% of source people have a C, thecurrent reference genome would only report an A at that position. Beyondsingle character changes, the current reference genome also fails toallow for larger-scale properties, such as regions with variable numbersof repetitions or positions known to have variable structuralrearrangements.

As indicated above, clinical WGS is dependent upon access to a referencegenome, which provides the framework upon which sequence variation canbe organized and reported. Much like solving a jigsaw puzzle, efficiencyis significantly improved by the availability of a picture of thecompleted jigsaw to guide placement. As shown in FIGS. 1A-1D, thecombined steps of alignment and variation calling are far from optimalas they fail to account for all available information and can productmultiple, distinct results. Thus, any calling procedure introducesbiases based on the reference genome used.

As an alternative to the current text-based reference genomes,graph-based models of DNA sequences have been explored. Graph modelsgenerally represent data using the concept of nodes and edges, whereclassically a node represents an observed property (e.g. a nucleotide atone position in a DNA sequence) and an edge represents movement from theprevious position to the next. A variety of graph types having beenintroduced in the computer science field. Several common graphstructures have been compared for their relevance to DNA sequenceanalysis (Kehr, B. et al. (2014) BMC Bioinformatics 15:99; incorporatedherein by reference in its entirety). Common graph types such as DeBruijn graphs and string graphs have been used in procedures for de novoread assembly (see, e.g., Flicek, P. et al. (2009) Nature 6(11Suppl):S6-S12; incorporated herein by reference in its entirety).

A graph-based reference genome has a number of advantages. It canrepresent all polymorphisms (recurrent variations) concurrently.Polymorphisms can be associated with a positional probability, allowingcorrelation between positions, as well as ethnic population differences(Dilthey, A. et al. (2015) Nature Genetics 47(6):682-8; incorporatedherein by reference in its entirety), to be represented in a singlegraph. Importantly, graph models have a universally unique ID for eachlocation (Paten B. et al. (2014) arXIV:1404.5010; incorporated herein byreference in its entirety) as more insertions and deletions arediscovered, allowing a reference to be updated as new data becomeavailable.

While a full reference genome based on graphs has not yet been created,efforts are underway to develop a human genome variation map as amathematical graph based on a De Bruijn graph, which represents DNAsequence as nodes. De Bruijn graphs are a compressed data structure.However, in most cases an adjunct data structure, such as read pairinformation, is needed to map reads onto the graph.

Despite the advances in generating graph-based models of referencesequences, many challenges remain. For example:

-   -   Linear representations allow for an unambiguous co-ordinate        system and, thus, defining distances is simple. Within a        flexible graph the represented components are relative and,        therefore, searching for a particular region within the genome        is a more complex problem.    -   Current annotations use the fixed linear co-ordinates system,        which may occur on multiple paths through the graph.        Accordingly, a graph reference genome would need to link the        annotations to all subgraphs that represent that section of the        reference.    -   The creation of randomized examples to serve as controls in an        experiment is difficult.    -   Updating the graph reference genome as new information is        discovered can be difficult due to the relative and flexible        nature of graph structures.    -   File formats and incompatibility with current software and tools        that are using the linear data structure create adoption        problems.    -   Graphs have only recently been used to perform read alignment on        genomic data and, therefore, there are fewer algorithms        developed that utilize graphs.    -   Ease of visualization for large datasets. It can be difficult to        view complicated non-planar data structures in a simple planar        form.

Another significant challenge with the current graph model methods isthe need for enormous storage requirements for computational analysis.Whereas DNA is diploid for humans (i.e., two copies of each chromosomewith one from each parent), each reference genome is haploid.Additionally, graph models do not account for the diversity of DNAsequence variation observed within and between populations. It has beenshown that using a population reference De Bruijn graphs that combinemultiple reference sequences as well as SNPs and Indels improves theaccuracy of alignment algorithms (Dilthey, A. et al. (2014) NatureGenetics 47(6):682-8). However, the human genomes used by popularalgorithms such as BOWTIE are approximately 2.3 GB in size without any“-omics” data. Hence, storing a complete picture of the human genomeusing current graph methods requires enormous storage and RAM. Thus,there remains a need for systems and methods to provide a referencegenome that would capture all polymorphisms, such as single nucleotidechanges, small insertions or deletions, and larger structural changessuch as regional duplications, inversions, or translocations, as well asthe correlations between all such variations, without creating an unduerequirement for data storage and processing capacity.

A key challenge in genome analysis is the computational scale of theproblems. Processing WGS can take multiple days on a multiple CPUsupercomputer. In 2011, D-Wave Systems announced the first commercialquantum annealer, a new approach to supercomputing. Quantum computersoptimize a function describing the system, over a set of candidatestates using fluctuations (i.e., changes in the energy at points of theseparable complex Hilbert space where the function operates). A quantumcomputer exploits superposition and entanglement, enabling it toconsider all possible states simultaneously. To illustrate, there areover 6 billion base pairs in a human cell, and each location comprisesof one of four nucleotides; hence, there are roughly 46 billion possiblestates. hese numbers are simply too big for classical computers unlesssignificant data compression techniques are used, which leads to loss ordistortion of information. This new development in technology offers achance to transform DNA analysis; to accelerate and improve the qualityof clinical results by simultaneously evaluating all possible states forreference DNA. There is, however, a major challenge related to thetechnology. The most advanced processors can only handle 256 qbits,which limits the capacity of the system to work with only small graphscomposed of a few hundred nodes. Accordingly, there is a need for agraph representation of the genome which sharply reduces the size.Likewise, there is a need for a graph representation that can beanalyzed using parallel computing techniques that are currentlyavailable until quantum computers become more powerful.

Other approaches to develop a graph representation of the genome includethe DISCOVAR algorithm, which uses a De Brujin graph in which observedDNA sequences are represented as edges (Weisenfeld, N. et al. (2014)Nature Genetics 46(12):1350-55; incorporated herein by reference in itsentirety). However, the assembly graph created using DISCOVAR does notgive a probabilistic weighting to the edges in accordance with other“-omics” data available. The assembly graph lacks the flexibility toselect known variants and therefore create an updated reference genomebased on known variations between populations, etc. The assembly graphis a unipath graph, which is a directed graph derived from the k-mergraph where each node represents a k-mer sequence. Furthermore, as ak-mer graph, the DISCOVAR procedure produces a compressed graph andrequires adjunct data structure to perform read alignment (such as readpair information) and is, therefore, not be suitable for use in quantumcomputing.

Despite the advances of the art in generating reference genomicsequences for assembly of short reads, there remains a need to produce areference graph that represents all relevant polymorphismssimultaneously in an efficient and compact manner to optimize datastorage and processing capacity, such as through quantum computing. Thepresent disclosure provides methods and systems that address these andrelated needs.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

In some embodiments, a computer-implemented method for updating a graphthat represents a portion of a reference genome is provided. Each nodeof the graph includes a sequence position, and edges of the graphinclude sequences of characters from a genomic alphabet. A mutationrecord is obtained that includes one or more mutation sequencesbeginning at a mutation sequence start position and ending at a mutationsequence end position. A minimal spanning graph is identified within thegraph that includes the sequence positions between the mutation sequencestart position and the mutation sequence end position. A mutation startnode is determined within the minimal spanning graph at the mutationsequence start position, and a mutation end node is determined withinthe minimal spanning graph at the mutation sequence end position. One ormore paths are identified beginning at the mutation start node andending at the mutation end node. Processing is performed for each pathof the one or more paths, for each first node and second node within thepath connected to each other by at least one edge, and for each mutationsequence of the one or more mutation sequences, wherein, in response todetermining that no existing edge between the first node and the secondnode includes a portion of the mutation sequence between the sequenceposition of the first node and the sequence position of the second node,a new edge is created connecting the first node to the second node; anda portion of the mutation sequence is added between the sequenceposition of the first node and the sequence position of the second nodeto the new edge. Any contradictory edges or superfluous edges areremoved from the graph after adding the new edges. The updated edges andnodes are stored in a graph data store.

In some embodiments, a computer-implemented method of aligning reads ofa read sequence to a graph that represents a genome and polymorphismstherein is provided. The graph includes a plurality of edges. A set ofbridges is selected from the graph. For each bridge in the set ofbridges, a subset of a read pool is selected, wherein reads in thesubset contain at least a portion of the bridge. For each read in thesubset, a local alignment is performed for the read, the local alignmentfor the read is scored to generate a read-bridge pair score; and theread-bridge pair score is inserted into a score matrix. The score matrixis used to determine a best combination of placements of reads for theset of bridges, and the reads are placed on the graph.

In some embodiments, a system for generating graphs based on referencegenome information is provided. The system comprises a graph data storeand at least one computing device. The graph data store is configured tostore a plurality of edge records, wherein each edge record includes astart node, an end node, a sequence listing, and a probability value.The at least one computing device is configured to obtain mutationrecords representing polymorphisms within the reference genome; andcreate and modify edge records within the graph data store based on themutation records.

In some embodiments, a system for performing read alignments to a graphthat represents a genome and polymorphisms therein is provided. Thesystem comprises a graph data store, at least one bridge computingdevice, a plurality of alignment computing devices, and at least onematrix processing computing device. The graph data store is configuredto store information representing the graph, the information including aplurality of edge records. The at least one bridge computing device isconfigured to receive a read pool; select a set of bridges from the edgerecords stored in the graph data store; for each bridge in the set ofbridges: select a subset of the read pool, wherein reads in the subsetcontain at least a portion of the bridge; and transmit reads from thesubset of the read pool and the bridge to an alignment computing device.The alignment computing devices are each configured to receive one ormore reads and a bridge with which the reads are associated; perform alocal alignment for each of the one or more reads; score the localalignment for each of the one or more reads to generate a read-bridgepair score for each of the one or more reads; and transmit theread-bridge pair scores to a matrix processing computing device. The atleast one matrix processing computing device is configured to: receiveread-bridge pair scores from the plurality of alignment computingdevices; insert the read-bridge pair scores into a score matrix; use thescore matrix to determine a best combination of placements of reads forthe set of bridges; and place the reads on the graph.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIGS. 1A-1D are sequence alignments that illustrate mapping a DNAsequence read to a reference genome sequence. The image is derived fromPaten B. et al. (2014) arXIV:1404.5010. Each sequence alignment in FIGS.1A-1D have the same reference sequence (SEQ ID NO:1) and allele sequence(SEQ ID NO:2), but with different gaps and mismatches assigned todifferent positions. FIGS. 1A and 1B both have 0 mismatches and 2 gapsopen (6 total gaps). FIGS. 1C and 1D both have a single gap open (6total gaps) and 2 mismatches. There is no optimal method to selectbetween the positions for the allele with respect to the referencegenome without further information not contained within the text-basedreference genome. The speed of alignment algorithms is a significantbottleneck to an analysis pipeline because the task of testing a readagainst all possible locations is computationally infeasible. Therefore,current algorithms often use a reference genome to find the most likelysection where the best mapping will be located, favoring speed overaccuracy. After a probable subset has been selected, slower algorithmswith higher accuracy are used to optimize placement of the read.

FIG. 2 illustrates a simple example of a mathematical graph structure.The graph has 7 nodes, and 10 edges. Each node is numbered, but notnecessarily sequentially. Edges connect nodes with “lengths”/“weights”shown by the numbers above each edge. The 6 edges with arrows aredirected edges (movement in one direction) and those without areundirected. The edge furthest to the left (with length 3) represents aloop where the start and end node are the same.

FIGS. 3A-3D illustrate four graph types depicting three distinct DNAsequences, with each sequence having eleven blocks. The image is derivedfrom Kehr, B. et al. (2014) BMC Bioinformatics 15:99, incorporatedherein by reference in its entirety. In each graph, the same threegenomes consisting of 11 blocks of co-linear sequences are aligned toeach other. In each of the graphs, it can be seen that there are 4blocks with no large structural changes. In the alignment graph (FIG.3A) there is a connection between the three genomes for each of theconserved blocks A, E, I and K. In the De-Bruijn (FIG. 3B) and enredo(FIG. 3C) graphs each of the three distinct paths pass linearly throughthese blocks, with the obvious extension that blocks A and K are sourceand sink nodes hence there are only edges exiting and entering,respectively. In the precursor cactus and cactus graph (FIG. 3D), theconserved edges represent singular connections between the largersubsections shown as the large grey circles, within which the structuralchanges are shown. The graphs also show structural rearrangements as theorder of the blocks in two of the three paths (the green and red graphs)are not alphabetical. Deletions are shown by a missing block, such asblock F for the red genome path and duplications are shown by repeatinga block such as block J also in the red genome path.

FIG. 4 schematically illustrates a De Bruijn graph of DNA sequenceassembly, ultimately achieving the sequence set forth as SEQ ID NO:3(see Berger, B., Peng, J., Singh, M. (2013) Nature Reviews: Genetics14:333-346, incorporated by reference herein in its entirety).

FIGS. 5A-5C are schematic representations of multiple sequence alignmentalgorithms used for reference construction. FIG. 5A illustrates fourindividual assembled genomes with mutations (labelled as light blue,purple, pink, and green) highlighted against the dark blue linearreference genome. FIG. 5B illustrates how the four individual genomesmay be merged to form a reference genome using existing multiplesequence alignment software. FIG. 5C illustrates a schematicrepresentation of the GGM approach to generating a reference sequencewith the sprouts algorithm. In this schematic, the dark blue linerepresents the linear human reference genome and additional data setsare added over depending on the order of linearity of the mutations. Thecoloured blocks stacked over the reference genome represent themutations from the individuals shown in FIG. 5A.

FIG. 6A is a representation of the sequence GAGCCTGGGAT[G/C]AAA (SEQ IDNO:4) using overlapping 3-mers as in a De Bruijn graph.

FIG. 6B is a representation of the same SEQ ID NO:4 using nonoverlapping 3-mers as in a De Bruijn graph.

FIG. 6C is a representation of the same SEQ ID NO:4 using the GNOmicsGraph Model (GGM) model showing how long conserved sequences can beplaced in the graph as a single edge which makes the graph more compactand hence more computationally-efficient.

FIGS. 7A-7G illustrates examples of simple sequence polymorphisms asdepicted using the GGM model of the present invention. FIG. 7Aillustrates the original sequence ATGACCGACGAGATGAAA (SEQ ID NO:5) splitbetween the nodes used later when the alternative alleles are included.FIG. 7B illustrates how a single nucleotide polymorphism,ATGACCGACGA[G/A]ATGAA (SEQ ID NO:6), would be represented in the GGMmodel. An edge (indicated as green) is inserted between nodes 6 and 7with the alternative allele as the edge label. FIG. 7C illustrates how adeletion, ATGACCGAC[GAG/-]ATGAAA (SEQ ID NO:7), would be represented. Anedge (indicated as blue) is inserted between nodes 5 and 7 of thereference sequence with an empty label. It is not necessary to connectthe empty edge to node 6 as the deletion spans the SNP. FIG. 7Dillustrates how an insertion, ATGACCGAC[CGACGACGA]GAGATGAAA (SEQ IDNO:8), would be represented. Repetitive elements are modelled as loopedges (indicated as yellow) in the graph. FIG. 7E illustrates how atranslocation within a chromosome ATG[GAGATGAAA][ACCGA] (SEQ ID NO:9),would be represented. Tracing from left to right, the path containingthe translocation travels along new edges edge from node 2 to node 5,labeled 1^(st) purple edge, continues along the reference graph untilnode 8, then travels back across the edge labeled 2nd purple to node 2and then through nodes 3 and 4 before traversing the final edge, labeled3^(rd) purple, connecting it to node 8 and completing the translocatedsequence. FIG. 7F illustrates how a single nucleotide polymorphisms onan existing edge, ATGACCGACGAGAT[G/C]AAA (SEQ ID NO:10), would berepresented in the GGM model. The existing edge is split by adding newnodes on either side of the mutation. An extra edge, labelled in red, isadded to represent the alternative allele for that mutation. FIG. 7Gillustrates the GGM model for all of the mentioned mutations in a singlecombined graph.

FIGS. 8A-8C schematically illustrate substructures in the GGM. FIG. 8Ashows two illustrative GGM graphs representing different substructures,e.g., an “orange” chromosome and a “blue” chromosome. The edges shown inred on the orange chromosome and pink on the blue chromosome representareas of the two chromosomes that are exchanged in an inter-chromosomaltranslocation. FIG. 8B illustrates the links between the two chromosomesat the break points of the translocation with the purple edges. FIG. 8Cillustrates the two graph are rearranged to form linked subgraphs withpurple edges showing the connections that represent the translocationbetween chromosomes.

FIG. 9 illustrates a representation of a whole genome graph where eachof the chromosomes can be a subgraph. This is an alternative to FIGS.8A-8C where the chromosomes were represented as linear subgraphs. Eachof the larger circles in FIG. 9 represents a more complex subgraph withthe dotted lines showing the sequential ordering and the solid linesshowing inter-subgraph mutations and rearrangements.

FIG. 10 is a schematic representation of the linearity of various typesof mutations.

FIG. 11 is a schematic of the pipeline for the GGM method. The twoalgorithms that generate the cost function and the reference GGM areCFgen and Sprouts, respectively.

FIG. 12 illustrates a subsection of chromosome 21 (17,000,000 to18,000,000) using the GGM model to indicate basic mutations (e.g., SNPsand short INDELS).

FIGS. 13A and 13B illustrate fixed edge k-mers (FEK). A FEK is a bridgebetween two nodes within the personalised reference GGM, which ifremoved results in a disjointed graph. A bridge is a path that connectsa node having no more than one outgoing edge to a node having no morethan one incoming edge. FIG. 13A illustrates a FEK with the hashedarrow. FIG. 13B illustrates a highly probable FEK, which is determinedduring the later stages of the alignment algorithm when one of multiplepossible edges is weighted heavily with a probability above a confidencethreshold, and edges weighted with a probability below the confidencethreshold are ignored when searching for FEKs.

FIGS. 14A-14C illustrate a comparison of a GGM to a Cactus graph. FIG.14A illustrates a manual recreation of the Cactus graph example (imageobtained from “Cactus graphs for genome comparison,” Paten et al., J.Comput. Biol. (2011) 18(3):469-81, incorporated by reference herein inits entirety) with the same blue and green paths shown. FIG. 14Billustrates a manually created GGM representation of the same sequencein FIG. 14A with the blue path highlighted. FIG. 14C illustrates amanually created GGM representation of the same sequence in FIG. 14Awith the green path highlighted.

FIGS. 15A-15C illustrate the personalisation of a reference genome for asmall section of chromosome 7 of the human genome. The super populationis Europe and the subpopulation is Tuscans in Italy. The standard edgeweights in FIGS. 15A-15C represent the global minor allele frequency.The indicated “red” edge weights introduced in FIG. 15B represent theallele frequencies for the European super population, as defined in theHapMap and 1000 genomes projects. The indicated “blue” edge weightsintroduced in FIG. 15C represent the allele frequencies for the Tuscansubpopulation, as defined in the HapMap and 1000 genomes projects.

FIG. 16 illustrates part of BRCA2 reference (Chr 13:32,340,400-32,340,455) generated with the GGM approach for basicmutations. Black edges represent the human reference genome, blue edgesrepresent insertions, red edges represent deletions, and green edgesrepresent SNV.

FIG. 17A illustrates the genotype-to-phenotype links for BRCA2 (Chr 13:32, 340, 400-32, 340, 455). FIG. 17B illustrates the meta-graph linkinggenotypes based on shared phenotypes where the edge thickness correlatesto the number of shared phenotypes.

FIG. 18 illustrates two reads (read 1 set forth as SEQ ID NO:11 and read2 set forth as SEQ ID NO:12) being mapped to the linear reference genome(SEQ ID NO:13) (top) and the same reads mapped to a GGM representationthat includes SNP information (SEQ ID NO:14) (bottom).

FIG. 19 is a block diagram that illustrates an exemplary embodiment of asystem for performing read alignments according to various aspects ofthe present disclosure.

FIG. 20 is a block diagram that illustrates various aspects of anexemplary computing device suitable for use with embodiments of thepresent disclosure.

DETAILED DESCRIPTION

The present disclosure provides a graph-based reference genome frameworkreferred to hereinafter as the GNOmics Graph Model (GGM) that canincorporate all known polymorphisms from standard data repositories,including SNPs, indels, and spatial and copy rearrangements, and relatedmethods and systems for generating the GGM. The graph can be paired witha correlation table of the relationships between polymorphisms within afixed distance, allowing for probabilistic determination of whichpositions are likely to show correlation in a sample.

As will be described in more detail below, the disclosed GGM methodprovides a graph model, and related methods and systems, for referencehuman genomes that use nodes for transitions and edges for sequence.Accordingly, reference genome constructed using the GGM method isdefined by edges that are used to represent sequences that areessentially immutable. Variations that are highly likely can berepresented as additional directional edges or nodes. A DNA sequence orsubsequence of any length can be affixed to an edge. In someembodiments, edge can be assigned a probabilistic weighting (orlikelihood) of the edge being present in genomic sample being assayed byWGS. The edge weighting can be inter-related with other edges dependingon the path chosen through the graph. Additionally, the graph of thepresent disclosure permits a non-linear path such as a cycle to betraced, thus allowing for the analysis of sequences containingrepetitive regions. In some embodiments, an interaction table isprovided that specifies the correlation between edges within apopulation.

As used herein, the term “graph” refers to an ordered pair G=(V, E)comprising a set V of nodes and a set E of edges, which are 2-elementsubsets of V. An edge is connects two nodes. FIG. 2 shows a simpleexample of a mathematical graph. Heretofore, graph models have generallyrepresented data using a node to represent an observed property (e.g., anucleotide at one position in a DNA sequence) and an edge representsmovement from the previous position to the next. Edges can be directed(indicating movement only in one direction) or undirected (indicatingmovement in both directions), and can be considered to have length.There are many types of graphs that have been developed in computerscience and mathematics, ranging from simple to complex.

The representation of DNA sequence using graph models has beenpreviously explored. FIGS. 3A-3D provide several common graph structures(i.e., text alignment (3A), De Bruijn (B), Enredo (C), and cactus (D))have been compared for their relevance to DNA sequence analysis, showingthat transformations between the most common forms are trivial,indicating common underlying similarities. FIG. 4 shows an example of aDe Bruijn graph, which have been used in procedures for de novo readassembly (i.e., genome sequence construction of short reads using areference genome) as well as early stage reference construction.

As indicated above, a graph-based reference genome provides a number ofanticipated advantages. It can represent all polymorphisms (i.e.,recurrent variations) concurrently. Polymorphisms can be associated witha positional probability, allowing correlation between positions, aswell as ethnic population differences, to be represented in a singlegraph. Importantly, graph models have a universally unique ID for eachlocation as more insertions and deletions are discovered, allowing areference to be updated as new data become available.

However, there are several challenges that currently exist in theconstruction of graph reference genomes. These drawbacks are describedin more detail above, and include issues with logical coordinatedesignations, the ability to update the reference genome graph with newinformation, file and system compatibilities with current software andgenomics tools that emphasize linear data structures, paucity ofalgorithms to align sequences to reference graphs, ease of visualizationfor non-planar data structures, difficulty of generating simulated andrandomized examples for controls, and storage and computationallimitations of current computer infrastructure in view of the enormoussize of data involved.

The present disclosure provides for an efficient and compact approachfor representing a reference genomic graph that addresses many of thesechallenges. The output of the disclosed graph approach is acomputational framework for the representation of a reference genomesequence, the assembly of experimental short sequencing reads using thereference genome, and the analysis of genetic observed geneticvariation. This technology is well suited for any organism in whichmultiple genome sequences are expected to be generated, includingmicrobes, endangered species, species of agricultural importance, aswell as humans and other vertebrates extensively used in research. Thegraph-based model of genetic variation created can be used for thedetection and analysis of DNA sequence variation (ranging from singlenucleotides polymorphisms to larger structural changes).

Embodiments of the present disclosure provide numerous technicaladvantages over previously attempted techniques. As one example, thegraph model disclosed herein provides for a more compact representationof genomic information than existing techniques. Compared to a De Brujingraph wherein neighboring sequence information is repeated in adjacentnodes, the present graph model uses less storage space because nosequence information is repeated in neighboring edges. As anotherexample, because the graph model disclosed herein uses a cyclic graph,repeated sequences can be compressed into a single repeating edgeinstead of requiring each repetition to be listed, thereby furtherreducing the required storage space. As a further example, thetechniques disclosed herein for performing a read alignment using thegraph model reduce the time needed for the read alignment because theyprovide the ability to use parallel computing resources to concurrentlyprocess multiple reads from read pools. As still another example, thegraph model disclosed herein provides enhanced visualization andanalysis characteristics compared to previous techniques. A key conceptunderlying the invention is the generation of a graph model for areference genome sequence uses nodes for transitions and edges forsequence. This is the reverse of classic approaches described above. Afull reference genome can be constructed using a graph in which edgesrepresent sequences that are essentially lack variation, and are thuscollapsed into a single edge representation. Polymorphisms that arelikely to occur, such as single or multiple nucleotide polymorphisms,insertions, deletions, rearrangements (e.g., translocations) can berepresented as additional directional edges or nodes. See, e.g., FIGS.7A-7G.

In some embodiments of the disclosed model, each of the edges carries aweight that is inter-related with other edges, depending on the pathchosen through the graph. This reflects the fact that certain portionsof the genome are linked, and tend to stay together over time. Thisphenomenon results in haplotype blocks that can be observed in thepopulation. Thus, the detection of a particular edge influences theassignment of a weight to a linked edge at a distinct location in thegraph.

As represented, each node is simply a placeholder within the graph butdoes not directly correlate to a particular base pair location. However,in an illustrative implementation, the nodes can have a position labelfrom the current reference genome GRCH38 to ease transitions andpopulation of the graph. The nodes do not have any associated weighting.A path through the graph represents a potential haploid referencegenome.

The disclosure provides a novel graph model representation thatovercomes limitations of established models, providing many benefits bycombining an edge labeled cyclic graph with a probabilistic costfunction based on known genetic information. Generally described, thefollowing characteristics are combined within the GGM realize thebenefits over existing graph models described above. First, DNA sequenceinformation is recorded as labels on the edges, rather than the commonuse of DNA sequence labels being affixed to nodes. DNA sequence of anylength of letters can be affixed to an edge and typically representstretches of reference sequence that have no, or likely to have low,variation in the reference population and, thus, can be collapsed into asingle edge representation to conserve computational andrepresentational resources. Edges can be assigned “costs” or weights,which relate to the probability of the edge being present in a sample,e.g., the probability of the target genome being sequenced will have theindicated sequence. This weight can be initially applied based on, forexample, known prevalence in a relevant reference population orsubpopulation. The weights can be adjusted in light of observedproperties during an analysis. The model allows for non-linear paths tobe traced and, thus permit illustration of cycles representing repeatingsegments. Finally, the model can include an interaction table (i.e., ameta-graph), which specifies the correlation between (i.e., the linkageor the co-occurrence of) edges within a population.

By shifting sequence to the edges of the graph and allowing any lengthof letters to be combined, long invariant segments of the genome can becompressed. The GGM is flexible and allows for simple addition ofvariants, by breaking an edge into two pieces by the insertion ofadditional nodes and/or edges. The flexibility of the model allows forrepresentation of cycles to indicate repeated structures and structuralrearrangements/inversions in a compact manner compared to theestablished graph models.

FIG. 19 is a block diagram that illustrates an exemplary embodiment of asystem for performing read alignments according to various aspects ofthe present disclosure. As illustrated, the GGM system includes a bridgecomputing device, a matrix processing computing device, a plurality ofalignment computing devices, and a graph data store. The graph datastore is configured to store one or more GGM graphs as discussed herein.The bridge computing device is configured to receive a read pool. Theread pool may be generated by a sequencing device, or may be obtainedfrom a data store. The bridge computing device selects a set of bridges(or FEKs) from a GGM graph stored in the graph data store. For eachbridge, the bridge computing device selects a subset of the read poolwherein the reads contain at least a portion of the bridge, andtransmits the subset of the read pool and the bridge to the plurality ofalignment computing devices for alignment. The alignment computingdevices perform local alignments for the reads and scores the localalignments to generate read-bridge pair scores. The local alignment maybe performed using any suitable technique, including but not limited tousing a Smith-waterman algorithm, dynamic programming, orposition-specific scoring matrices. The alignment computing devices thentransmit the read-bridge pair scores to the matrix processing computingdevice, which adds the scores to a score matrix, and uses the scorematrix to determine a best combination of placements of reads for theset of bridges. The best combination may be determined using anysuitable technique, including but not limited to performing aneigenvalue decomposition, a spectral mapping, or a functional analysisusing Hilbert or Banach spaces. The reads are then placed on the graph,and the alignment may be stored in the graph data store.

In some embodiments, some of the illustrated computing devices, such asthe bridge computing device, the matrix processing computing device,and/or a computing device that provides the graph data store, may becombined into a single computing device. In some embodiments, thefunctionality of one or more of the illustrated computing devices may beseparated into multiple computing devices. In some embodiments, theillustrated computing devices may be communicatively coupled to eachother over any type of suitable network or other communicationtechnology.

FIG. 20 is a block diagram that illustrates aspects of an exemplarycomputing device 2000 appropriate for use with embodiments of thepresent disclosure. While FIG. 20 is described with reference to acomputing device that is implemented as a device on a network, thedescription below is applicable to servers, personal computers, mobilephones, smart phones, tablet computers, embedded computing devices, andother devices that may be used to implement portions of embodiments ofthe present disclosure. Moreover, those of ordinary skill in the art andothers will recognize that the computing device 2000 may be any one ofany number of currently available or yet to be developed devices.

In its most basic configuration, the computing device 2000 includes atleast one processor 2002 and a system memory 2004 connected by acommunication bus 2006. Depending on the exact configuration and type ofdevice, the system memory 2004 may be volatile or nonvolatile memory,such as read only memory (“ROM”), random access memory (“RAM”), EEPROM,flash memory, or similar memory technology. Those of ordinary skill inthe art and others will recognize that system memory 2004 typicallystores data and/or program modules that are immediately accessible toand/or currently being operated on by the processor 2002. In thisregard, the processor 2002 may serve as a computational center of thecomputing device 2000 by supporting the execution of instructions.

As further illustrated in FIG. 20, the computing device 2000 may includea network interface 2010 comprising one or more components forcommunicating with other devices over a network. Embodiments of thepresent disclosure may access basic services that utilize the networkinterface 2010 to perform communications using common network protocols.The network interface 2010 may also include a wireless network interfaceconfigured to communicate via one or more wireless communicationprotocols, such as WiFi, 2G, 3G, LTE, WiMAX, Bluetooth, and/or the like.

In the exemplary embodiment depicted in FIG. 20, the computing device2000 also includes a storage medium 2008. However, services may beaccessed using a computing device that does not include means forpersisting data to a local storage medium. Therefore, the storage medium2008 depicted in FIG. 20 is represented with a dashed line to indicatethat the storage medium 2008 is optional. In any event, the storagemedium 2008 may be volatile or nonvolatile, removable or nonremovable,implemented using any technology capable of storing information such as,but not limited to, a hard drive, solid state drive, CD ROM, DVD, orother disk storage, magnetic cassettes, magnetic tape, magnetic diskstorage, and/or the like.

As used herein, the term “computer-readable medium” includes volatileand non-volatile and removable and non-removable media implemented inany method or technology capable of storing information, such ascomputer-readable instructions, data structures, program modules, orother data. In this regard, the system memory 2004 and storage medium2008 depicted in FIG. 20 are merely examples of computer-readable media.

Suitable implementations of computing devices that include a processor2002, system memory 2004, communication bus 2006, storage medium 2008,and network interface 2010 are known and commercially available. Forease of illustration and because it is not important for anunderstanding of the claimed subject matter, FIG. 20 does not show someof the typical components of many computing devices. In this regard, thecomputing device 2000 may include input devices, such as a keyboard,keypad, mouse, microphone, touch input device, touch screen, tablet,and/or the like. Such input devices may be coupled to the computingdevice 2000 by wired or wireless connections including RF, infrared,serial, parallel, Bluetooth, USB, or other suitable connectionsprotocols using wireless or physical connections. Similarly, thecomputing device 2000 may also include output devices such as a display,speakers, printer, etc. Since these devices are well known in the art,they are not illustrated or described further herein. Unlessspecifically defined herein, all terms used herein have the same meaningas they would to one skilled in the art of the present invention.

As understood by one of ordinary skill in the art, a “data store” asdescribed herein may be any suitable device configured to store data foraccess by a computing device. One example of a data store suitable foruse with the high capacity needs of the systems disclosed herein is ahighly reliable, high-speed relational database management system(RDBMS) executing on one or more computing devices and accessible over ahigh-speed network. However, any other suitable storage technique and/ordevice capable of quickly and reliably providing the stored data inresponse to queries may be used, such as a key-value store, an objectdatabase, and/or the like. Further, the computing device or devicesproviding the data store may be accessible locally instead of over anetwork, or may be provided as a cloud-based service. A data store mayalso include data stored in an organized manner on a computer-readablestorage medium. One example of a data store which includes reliablestorage but also low overhead is a file system or database managementsystem that stores data in files (or records) on a computer-readablemedium such as flash memory, random access memory (RAM), hard diskdrives, and/or the like. One of ordinary skill in the art will recognizethat separate data stores described herein may be combined into a singledata store, and/or a single data store described herein may be separatedinto multiple data stores, without departing from the scope of thepresent disclosure.

The use of the term “or” in the claims is used to mean “and/or” unlessexplicitly indicated to refer to alternatives only or the alternativesare mutually exclusive, although the disclosure supports a definitionthat refers to only alternatives and “and/or.”

Following long-standing patent law, the words “a” and “an,” when used inconjunction with the word “comprising” in the claims or specification,denote one or more, unless specifically noted.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is, to indicate in the sense of“including, but not limited to.” Words using the singular or pluralnumber also include the plural and singular number, respectively.Additionally, the words “herein,” “above,” and “below,” and words ofsimilar import, when used in this application, shall refer to thisapplication as a whole and not to any particular portions of theapplication.

Publications cited herein and the material for which they are cited arehereby specifically incorporated by reference in their entireties.

The following examples are provided for the purpose of illustrating, notlimiting, the material disclosed herein.

EXAMPLES Example 1

This example describes the storage of DNA sequences as edge labels on adirected connected graph, which can represent a reference genomecontaining common variants observed for a species or a sub-population ofa species.

Unlike De Bruijn graphs, the GNOmics Graph Model (GGM) approach of thecurrent invention does not display overlap in the sequence label betweenadjacent edges. This is because each polymorphism is represented by aunique edge within the subgraph correlating to that sequence. In FIG. 6Athe sequence requires 8 nodes and 8 edges using a De Bruijn graphstructure with 3-mers that overlap by 1. Removing the overlap of theillustrated k-mers reduces the number of nodes and edges to six each.See FIG. 6B. A further reduction can be gained by using the GGM model,as shown in FIG. 6C, which only requires 4 nodes and 4 edges. The resultof implementing the GGM is a mutable graph reference genome thatincorporates all known polymorphisms from standard data repositories,including SNPs, indels, and spatial and copy rearrangements paired witha correlation table of the relationships between polymorphisms within afixed distance. By selecting characteristics such as population(Dilthey, A. et al. (2015) Nature Genetics 47(6):682-688; incorporatedherein by reference in its entirety), a personalized graph referencegenome is created for more accurate read alignment.

The present GGM approach (also referred to herein as “GRAPH”) results inthe directed connected graph M consisting of the directed edges E andthe vertices V, i.e., M=(V, E).

For the representation of genome sequence variation, the GGM approachprovides a method to store genomic sequence as edge labels on a directedconnected graph, which represents a reference genome with commonvariations for a species or population. The capacity to represent allvariation types within the same framework is an important advancecompared to existing graph models. The approach allows for longstretches of non-variable sequence to be compacted into a single edge,thereby reducing the number of nodes and edges dramatically and as aconsequence reduces the computational requirements needed for sequenceanalysis.

Each edge has an associated transition probability or edge weight, and alabel which represents a DNA sequence of any number of nucleotides. Thelength of an edge is defined as the number of nucleotides on the label.An edge label may be empty, which represents a transition without anyassociated sequence length. An edge has a primary direction whichmatches with reading the label from left to right (e.g., 5′ to 3′ for aDNA sequence). If an edge is traversed in reverse of its primarydirection then the label sequence is replaced by its reverse complementsequence (e.g., 5′-CAGT-3′ becomes 5′-ACTG-3′). Each vertex may belabelled with the associated base pair coordinate from one or moretext-based reference genomes for the species being studied, e.g., GRCH37and GRCH38 for humans, corresponding to the coordinate of the next edgelabel nucleotide represented in the text-based genome. This enablescross compatibility with text-based reference genomes.

Example 2

This example describes how the use of the GGM allows the representationof sequence variations.

The GGM approach allows for the simple introduction of sequencevariants, by breaking an edge into two pieces. Other sources of sequencevariation such as structural rearrangement, repeated sequence elementsand inversions can be accommodated by using cycles. FIGS. 7A-7Gillustrate the methods used to represent different mutations using theGGM approach including but not limited to single character mutations,insertions, deletions, inversions, intra-translocation,inter-translocation and copy number variations. Sub-structures ofexisting reference genomes, such as chromosomes, can be represented assubgraphs (see FIGS. 8A and 8B), wherein the subgraphs are connectedlinearly to establish an order of the substructures as shown in FIG. 8C(e.g., by chromosome number). However, the subgraphs may also beconnected across substructures if such genetic variations are observedthat span multiple substructures, as shown in FIG. 9.

Example 3

This example describes the comparison between the cactus graph model andthe GGM.

For comparison of the GGM to an existing graph model, the same sequenceregion is displayed using a cactus graph (FIG. 14A) and the GGM (FIGS.14B and 14C). The illustration delineates two alleles for the sameregion (a “green” allele and a “blue” allele), where one allele isanticipated to be derived from each parent. The cactus graph includes 37nodes and 36 edges, whereas the GGM uses 17 nodes and 31 edges torepresent the same number of characters. Most approaches to genomealignment and construction using graph structures use the idea oftracing a path through the graph to generate the linear representationof the genomic sequence. Dijkstra's algorithm is one of the mostwell-known algorithms for finding the shortest paths between nodes in agraph and it has a running time of O(|V|2) with some improvements madefor special cases of graphs. Therefore, any reduction in the number ofnodes in a graph will dramatically reduce the running time for shortedpath algorithms. It is evident that an overall reduction in both nodesand edges will reduce the storage requirements for a graph.

Example 4

This example describes an illustrative algorithm for the creation of aGGM.

An illustrative algorithm used for the GGM approach is called Sproutsand is based on the classical computer science problem known as “Game ofSprouts.” The concept is that the GGM is sprouting and, hence, is builtfrom a bottom-up approach. In traditional multiple sequence alignment(MSA) algorithms used for reference construction, the complete sequencesof multiple individuals are merged at places where there is novariation, thus creating a single reference sequence that is mostrepresentative. This process is depicted pictorially in FIGS. 5A and 5B.In contrast, with the sprouts algorithm, the smallest data set is usedand additional data sets are added on top in accordance with the orderof linearity of the mutations, as shown pictorially in FIG. 5C. Eachtime a new mutation is added to the model it creates a new possible pathin the reference GGM model. In this manner, this allows the mutationsincluded in the reference GGM to be constrained by type, size or otherattributes.

In order to automate the process, the linearities of mutations aredefined within the GGM approach as shown in FIG. 10. Linear mutationsare defined as single forward edges between adjacent nodes in ascendingorder. Examples of linear mutations include bridges in the graph withconserved sequences and no known mutations. Semi-linear mutations, whichinclude mutations with no overlap to other mutations such as SNPs andINDELS, are defined as multiple forward edges between adjacent nodes inascending order. Forward semi-linear mutations are defined as the startof a region with multiple overlapping mutations. These are depictedwithin the GGM as multiple forward edges between a single node andhigher nodes. Backward semi-linear mutations correspond to the end of aregion with multiple overlapping mutations and are represented asmultiple forward edges from multiple lower nodes to a single node.Non-linear mutations are defined as multiple unordered incoming andoutgoing edges, which can include loops representing sequence repeats orinsertions, as well as highly mutated regions.

The reference string is generated by, for example, concatenating themultiple lines of a fasta file or using known existing referenceco-ordinates. This reference string is set as a simple graph, with twonodes and a labeled edge representing the entire string. If the stringis too large to be loaded on the computer, then the algorithm can beconverted to work under a divide and conquer method, creating subgraphsfor smaller regions and then merging the graphs afterwards.

If the mutations are provided as a list of known mutations from standardpublic databases, then a file (e.g., a vcf file) is created from theGNOmics database. Otherwise an input file (e.g., a vcf file) given isformatted to select the following information:Chr, start_bp, stop_bp, strand, var_key, prefix, id, type, ref_allele,alt_ 1_allele, alt_2_allele, alt_3_allele

The file is read by individual lines, allowing for furtherparallelisation. The file can be converted so that each mutation isdefined for the positive strand of the reference sequence should therebe multiple strands.

For each type of mutation, the nearest start and end nodes areidentified in the graph, and if necessary new nodes are created torepresent the mutations start and end point and the original referencesequence is split around the new nodes. New edges are added to representthe alternative alleles for each mutation with rsnum, weight, mutationtype, and colour as attributes. The rsnum allows the mutation to belinked to current databases. The colour is based on the mutation typewhich is inputted from the vcf file.

To update the GGM as new genetic information is received, the linearityof the mutation is determined. If coordinate information is known, forexample, if the GRCH37/38 coordinates are known, then the mutation canbe parsed through the Sprouts algorithm. If coordinates are not known,then flanking sequence information can be used to select subgraphcontaining the region.

Example 5

This example describes the construction of an illustrative GGM forchromosome 21.

Using the GGM approach described herein, a model of the human chromosome21 was developed that incorporated all known single nucleotide variants,insertions and deletions. The computation pipeline used is depicted inFIG. 11 where the sprouts algorithm described above was used toconstruct the model of the human chromosome 21 using the linearreference sequence and mutation information. FIG. 12 shows a small partof the chromosome 21 GGM showing edges that represent basic mutationsusing single nucleotide polymorphism data obtained from dbSNP. In orderto include structural mutations, data was collected from publicrepositories and using a basic reference GGM for the region, eachmutation was passed through the sprouts algorithm to identify theaffected subgraph and nodes and edges were inserted appropriately (FIG.18).

Example 6

This example describes the determination of edge weightings within thegraph using a probabilistic cost function that combines knowninformation.

As shown in FIG. 11, the Sprouts algorithm is used to generate thereference GGM model and the CFgen (Cost Function generator) algorithm isused to calculate the probabilistic cost function. Multiple phenotypicdatasets observed for an individual can be combined using CFGen tocreate edge weightings on a “personalised” reference GGM. For theinitial implementation, the CFgen algorithm simply assigns edgeweightings based on the minor allele frequencies of individual mutationsas indicated in publically available databases, such as provided by theHapMap and 1000 genomes projects. The edge weightings represent theprobability of observing that allele in a sample from the population ofthe “personalised” reference GGM model. FIG. 15 illustrates thepersonalization of a reference genome for a small section of the humanchromosome 7. The graph shows four standard SNPs (i.e., with NCBIreference ids: rs158, rs170, rs157, rs172) found in both the most recenthuman reference genomes (the GRCH38 and GRCH37 co-ordinates areindicated in the node labels) that have population-specific allelefrequencies given by the HapMap project. The edges between the start andend nodes for each mutation have 3 attributes: a sequence, a weighting,and a reference ID. The indicated sequence represents the allele forthat mutation. The weighting is the observed frequency of that allelewithin a population and the reference ID is taken from the publicdatabase dbSNP. The sequences between the SNPs are not shown for ease ofillustration as they are very long and contain other more complexmutations. The weights representing the global minor allele frequencyare represented in FIG. 15A. The “red” edge weights introduced in FIG.15B reflect the super population of Europe as defined in the HapMap and1000 genomes projects. The “blue” edge weights introduced in FIG. 15Creflect the subpopulation of Tuscans in Italy as defined in the HapMapand 1000 genomes projects.

In the graph represented in FIG. 15A, only the global population isknown and so all the edge weights are “black”. In the middle graph thesuper population is known (i.e., Europe) and so where there is availableinformation the edge weights are changed to those found in the superpopulation. See FIG. 15B.

In FIG. 15C, the sub population is known (i.e., Tuscans in Italy) and,hence, for each SNP, available frequencies for the subpopulation areused as an edge weight. If there is no information for the definedsub-population but there is information for an applicable superpopulation, then the frequency for the super population is used as theedge weight. If no information is available then the global allelefrequency is used. If there is no information at any level for theallele, then the edge weightings for that mutation are either equallydistributed or can be biased towards the reference allele. Thoroughtesting of population bias while using the GGM and the FEKs alignmentalgorithm will allow for the correct edge weightings to be generated.

The cost function generator algorithm can be expanded to includemultiple input phenotypic datasets, such as GWAS, disease specificmutation rates, and error rates of sequencing technology. Using atraining set, machine learning techniques can be generated to create abiased nonlinear function of all input information in order to weightthe edges.

As addition to individual edge weightings, the GGM contains a sparseinteraction matrix using meta information. This allows the GGM to beiteratively updated during read alignment or analysis. For example, ifan allele is observed, then all linked alleles are given an increasedweighting to reflect that the alleles are frequently observed together.The meta information incorporated into the model can include informationrelated to genome-wide association studies, phenotype information,phasing information, parental genetic information, linkage equilibrium,and the like.

Example 7

This example describes an illustrative use of meta-information to defineinteractions between nodes and edges in the GGM.

Meta-information can include, but is not limited to: genome wideassociation studies (GWAS), phenotype information, phasing information,parental genetic information, and linkage disequilibrium information. Inaddition to generated individual edge weightings, the GGM can contain asparse interaction matrix using meta-information. This allows the GGM tobe iteratively updated during read alignment or analysis. If an alleleis observed, then all linked alleles are given an increased weighting toreflect that the alleles are frequently observed together.

As shown in FIGS. 17A and 17B, a full implementation of the GNOmicsDatabase and Sprouts algorithm exists for the BRCA2 gene withmeta-information from mutations associated with the diseased gene.Specifically, FIG. 17A illustrates the genotype-to-phenotype links forBRCA2 (Chr 13: 32,340,400-32,340,455), whereas FIG. 17B illustrates themeta-graph linking genotypes based on shared phenotypes where the edgethickness correlates to the number of shared phenotypes.

Example 8

This example describes performing alignments of individual reads from aread sequence to a reference GGM to find the optimal combined alignmentof the set of sequences.

Traditional read alignment algorithms treat single or paired readsgenerated from sequencing machines individually and find the optimalalignment for each individual read (or paired reads). In contrast, theGGM approach uses a FEKs (fixed edge k-mers) algorithm. The readalignment is performed iteratively using subsets of the set of the inputreads, which are also referred to in aggregate as the read pool. Also,unlike existing methods that index the reference graph and use the readto search within the index, the GGM FEKs algorithm searches for GGMfixed edge k-mers (FEK) within members of the indexed read pool.

An edge k-mers (FEK) is defined as a bridge between two nodes within thepersonalised reference GGM, where removal of the bridge would result inbreaking or disjoining of the graph. For example, the hashed edge inFIG. 13A is a FEK (or “bridge”) because the graph disjoint if it wereremoved from the graph. A subset of the read pool is generated with theindividual reads that contain (or partially contain) the FEK sequence. Asingle read can be placed in multiple subsets as the subsets are notdisjoint. For each subset, a local alignment is performed and scored foreach read in the subset to generate a set of read-FEK pair (or“read-bridge pair”) scores. The scoring process in the algorithm can beperformed for each subset in parallel to enhance efficiency and speed.Once all read-FEK pair scores are calculated, they are combined in amatrix and using the meta-information interaction values, the bestcombination of placements is chosen for the reads contained within allthe read pools. Any suitable technique may be used to determine the bestcombination of placements of the reads using the matrix, including butnot limited to an eigenvalue decomposition, a spectral mapping, and afunctional analysis using Hilbert or Banach spaces. Any single read canonly be assigned to a single reference FEK, although any one FEK canhave multiple reads from the read pool assigned to it.

Once the reads are aligned to the graph, contradictory edges andsuperfluous edges are pruned from the reference GGM. The process isrepeated using new FEKs that may arise after the pruning state.Additionally, highly probable FEKs, where the FEK is a bridge containingan edge with a weight above a defined threshold, can also be used. Asshown in FIG. 13B, the three hashed edges are merged and considered tobe a highly probable FEK in the second stage of the alignment in view ofthe high weight assigned to the A SNP between the 3^(rd) and 4^(th)nodes. After each stage, a new set of highly probable FEKs is generatedfrom the previously pruned GGM and the threshold for a qualifying highlyprobably FEK can be lowered to generate larger subsets.

The FEKs algorithm is an iterative algorithm that can be optimised forless powerful computers using mass parallelisation when calculatingscores for each stage. The algorithm ends when the subsets are too smallfor combined alignment. At such a point, each remaining, unassigned readis treated as a subsequence to be found in the GGM.

For a specific individual's genome, the GGM is generated and thereference graph is iteratively pruned using FEKs as seed points fortracing the most probable path. The meta-information interaction matrixcan be used to update the edge weights as the seeded paths aregenerated. If an edge with known interactions is selected due to thealignment of reads, the weights of associated edges that have not beentraced are recalculated to include a weighting representing acorrelation between the two edges.

Using the GGM as a reference structure onto which reads are alignedprovides many benefits over the current linear text referencestructures. The GGM holds extensive amounts of known data about commonand rare variants. This means that if two alleles are almost as likelyat a particular position (e.g., where the major allele is present in 51%and the minor allele in 49% of a population), then the GGM could stillalign to the less common form (i.e., minor allele) perfectly at thatposition, whereas a linear reference would have indicated a mismatch.

Moreover, the GGM can be used to represent a customised referencegenome, which allows the edge weightings to be differently customisedbetween populations. In contrast, a linear reference genome imposessignificant bias towards the reference used. Accordingly, there islikely to be a significant reduction in bias towards the reference usedduring alignment of individuals from two separate populations to apersonalised reference GGM.

When performing an alignment using the FEKs algorithm, not only is aplethora of known variants being considered within the reference model,but an alignment of multiple reads is being performed simultaneouslyrather than treating each read (or read pair) sequentially as anindependent entity. For example, the top of FIG. 19 illustrates analignment to a linear reference where two reads treated independentlyboth map to positions A and B with equal likelihood due to twomismatches. However, when considered together on a GGM reference (seebottom of FIG. 19), read 1 maps to position A and read 2 maps toposition B because the GGM contains additional information of a minorSNP alleles that are matched differently by the reads. Therefore, eachread is treated as a partial match to the corresponding minor allelerather than an outright mismatch.

Example 9

This example describes phasing using the GGM approach.

Phasing is the process of determining the two allele sequences from theunordered combination of genotypes at each site. When approaching theproblem from graph theory point of view, there is an easy transitionfrom tracing one path through the graph representation of anindividual's genome to tracing two paths. While the GGM approach worksfrom this basic concept, it differs significantly from other algorithmsthrough the use of the meta-graph and read depth to predict the alleleswithin particular subgraphs and edges in the GGM of an individual'sgenome once the alignment is complete.

Personalised reference GGMs are created for each parent using eitherphenotype information or aligned sequence information. At places in thechild's genome where there are homozygous mutations, the SNPs can beused as seeds for the parental reference GGMs. The seeds are used toprune the parental reference GGMs by taking into consideration themeta-graph of linked edge information. This iterative process allows theparental reference GGMs to be reduced in complexity because highlyunlikely or impossible edges are pruned. After seeding the parentalreference genome, the process is reversed using homozygous positions inthe parental genomes to seed into the child's genome. Statisticalinferences can be made using the edge weightings of the parental graphsto determine which allele is more likely to have come from which parentin the diploid GGM representation of the child.

This technique is particularly effective in cases where the parents arefrom different populations with different phenotypes and, hence, theparents' reference GGMs will differ more significantly than if they arefrom the same population.

Example 10

This example describes variant discovery.

Variant calling is a natural second stage of the FEKs algorithm. Whenaligning the reads an individual's GGM representation of their genomewill be created and new edges will be added to the GGM when a variantnot observed in the initial personalised reference GGM is discovered inthe individual.

Further Examples

Further illustrative, non-exclusive examples of descriptions of somemethods and systems in accordance with the scope of the presentdisclosure are presented in the following numbered paragraphs. Thefollowing paragraphs are not intended to be an exhaustive set ofdescriptions, and are not intended to define minimum or maximum scopes,or required elements or steps, of the present disclosure. Rather, thenumbered paragraphs are provided as illustrative examples of selectedmethods and systems that are within the scope of the present disclosure,with other descriptions of broader or narrower scopes, or combinationsthereof, not specifically listed herein still being within the scope ofthe present disclosure.

X1. A computer-implemented method for updating a graph that represents aportion of a reference genome, wherein each node of the graph includes asequence position, and wherein edges of the graph include sequences ofcharacters from a genomic alphabet, the method comprising:

obtaining a mutation record that includes one or more mutation sequencesbeginning at a mutation sequence start position and ending at a mutationsequence end position;

identifying a minimal spanning graph within the graph that includes thesequence positions between the mutation sequence start position and themutation sequence end position;

determining a mutation start node within the minimal spanning graph atthe mutation sequence start position and a mutation end node within theminimal spanning graph at the mutation sequence end position;

identifying one or more paths beginning at the mutation start node andending at the mutation end node;

for each path of the one or more paths:

-   for each first node and second node within the path connected to    each other by at least one edge, and for each mutation sequence of    the one or more mutation sequences:    -   in response to determining that no existing edge between the        first node and the second node includes a portion of the        mutation sequence between the sequence position of the first        node and the sequence position of the second node:        -   creating a new edge connecting the first node to the second            node; and        -   adding a portion of the mutation sequence between the            sequence position of the first node and the sequence            position of the second node to the new edge;

removing any contradictory edges or superfluous edges from the graphafter adding the new edges; and

storing the updated edges and nodes in a graph data store.

X2. The method of Example X1, further comprising determining themutation sequence start position and the mutation sequence end positionusing sequence position information in the mutation record or usingflanking sequence information.

X3. The method of Example X1, wherein the genomic alphabet representsDNA nucleotides, RNA nucleotides, or protein amino acids.

X4. The method of Example X1, wherein creating the new edge connectingthe first node to the second node includes adding a probability value tothe new edge based on probability information within the mutationrecord.

X5. The method of Example X4, wherein creating the new edge connectingthe first node to the second node further includes updating probabilityvalues of other edges connecting the first node and the second node toaccount for the probability value added to the new edge.

X6. The method of Example X4, wherein the probability values areassociated with population information.

X7. The method of Example X6, wherein populations are organized into ahierarchy that includes a global population, a set of super populations,and a set of sub populations.

X8. The method of Example X6, wherein populations indicate separatephenotypic groups.

X9. The method of Example X8, wherein a phenotypic group includessubjects identified as possessing or having an increased probability ofpossessing a common trait, feature, symptom, disease, or condition.

X10. The method of Example X1, wherein edges of the graph includeidentifiers for locating a particular sequence in a public datarepository.

X11. The method of Example X10, wherein the identifiers are ReferenceSNP cluster IDs (rs numbers), European Bioinformatics Institute (EBI)structural variant numbers (esv numbers), or National Center forBiotechnology Information (NCBI) structural variant numbers (nsvnumbers).

X12. The method of Example X1, wherein groups of edges in the graph areassociated in a correlation data store.

X13. The method of Example X12, wherein creating the new edge connectingthe first node to the second node includes updating associations in thecorrelation data store that are affected by the creation of the newedge.

X14. The method of Example X12, wherein removing any contradictory edgesor superfluous edges from the graph after adding the new edges includesupdating associations in the correlation data store that are affected bythe removal of the contradictory edges or the superfluous edges.

X15. The method of Example X1, wherein the mutation start node and themutation end node are the same node.

X16. The method of Example X15, wherein the new edge includes a valueindicating a number of repetitions of the sequence of the new edge.

X17. The method of Example X1, wherein the sequence of the new edgecontains zero characters.

X18. The method of Example X1, wherein each edge is directed, andwherein traversing an edge in reverse of its direction causes thesequence of the edge to be interpreted as a reverse complement of thesequence.

X19. The method of Example X1, wherein the minimal spanning graph beginsat a spanning graph start node and ends at a spanning graph end node,and wherein determining the mutation start node within the minimalspanning graph at the mutation sequence start position includes:

determining that no node exists within the minimal spanning graph at themutation sequence start position;

creating a new node for the mutation start node, wherein the sequenceposition of the new node is the mutation sequence start position.

X20. The method of Example X19, wherein the sequence position of the newnode is between a sequence position of a region of interest start nodeand a sequence position of a region of interest end node, wherein asubgraph between the region of interest start node and the region ofinterest end node includes all paths that include the mutation sequencestart position, wherein the region of interest start node and the regionof interest end node are connected by one or more paths, wherein eachpath includes a path sequence defined by the sequences of edges withinthe path, and wherein the method further comprises, for each path havinga path sequence with a length greater than zero:

creating a first edge from a node before the mutation sequence startposition on a path starting at the region of interest start node to thenew node;

adding a sequence to the first edge that includes a portion of the pathsequence between the sequence position of the region of interest startnode and the mutation sequence start position;

creating a second edge from the new node to a node after the mutationsequence start position on a path ending at the region of interest endnode; and

adding a sequence to the second edge that includes a portion of the pathsequence between the mutation sequence start position and the sequenceposition of the region of interest end node.

X21. The method of Example X20, further comprising removing the edges ofthe paths having path sequences with a length greater than zero that donot pass through the new node.

X22. The method of Example X20, further comprising adding probabilityvalues to the first edge and the second edge based on probability valuesof the edges of the path.

X23. The method of Example X1, wherein the minimal spanning graph beginsat a spanning graph start node and ends at a spanning graph end node,and wherein determining the mutation end node within the minimalspanning graph at the mutation sequence end position includes:

determining that no node exists within the minimal spanning graph at themutation sequence end position;

creating a new node for the mutation end node, wherein the sequenceposition of the new node is the mutation sequence end position.

X24. The method of Example X23, wherein the sequence position of the newnode is between a sequence position of a region of interest start nodeand a sequence position of a region of interest end node, wherein asubgraph between the region of interest start node and the region ofinterest end node includes all paths that include the mutation sequenceend position, wherein the region of interest start node and the regionof interest end node are connected by one or more paths, wherein eachpath includes a path sequence defined by the sequences of edges withinthe path, and wherein the method further comprises, for each path havinga path sequence with a length greater than zero:

creating a first edge from a node before the mutation sequence endposition on a path starting at the region of interest start node to thenew node;

adding a sequence to the first edge that includes a portion of the pathsequence between the sequence position of the region of interest startnode and the mutation sequence end position;

creating a second edge from the new node to a node after the mutationsequence end position on a path ending at the region of interest endnode; and

adding a sequence to the second edge that includes a portion of the pathsequence between the mutation sequence end position and the sequenceposition of the region of interest end node.

X25. The method of Example X23, further comprising removing the edges ofthe paths having path sequences with a length greater than zero that donot pass through the new node.

X26. The method of Example X23, further comprising adding probabilityvalues to the first edge and the second edge based on probability valuesof the edges of the path.

X27. The method of Example X1, further comprising:

obtaining a plurality of mutation records; and

subdividing the plurality of mutation records into disjoint subsets thathave no overlap between the affected sequence locations.

X28. The method of Example X27, further comprising concurrentlyprocessing mutation records from the disjoint subsets.

X29. The method of Example X27, further comprising subdividing theplurality of mutation records into mutation types by linearity orcomplexity.

X30. A computer-implemented method of aligning reads of a read sequenceto a graph that represents a genome and polymorphisms therein, whereinthe graph includes a plurality of edges, the method comprising:

selecting a set of bridges from the graph;

for each bridge in the set of bridges:

-   selecting a subset of a read pool, wherein reads in the subset    contain at least a portion of the bridge; and-   for each read in the subset:    -   performing a local alignment for the read;    -   scoring the local alignment for the read to generate a        read-bridge pair score; and    -   inserting the read-bridge pair score into a score matrix;

using the score matrix to determine a best combination of placements ofreads for the set of bridges; and

placing the reads on the graph.

X31. The method of Example X30, wherein selecting the set of bridgesfrom the graph includes selecting at least one edge from the graph thatconnects a node having no more than one outgoing edge to a node havingno more than one incoming edge.

X32. The method of Example X31, further comprising selecting asubsequent set of bridges from the graph.

X33. The method of Example X32, further comprising pruning contradictoryedges and superfluous edges from the graph before selecting a subsequentset of bridges from the graph.

X34. The method of Example X32, wherein selecting at least one edge fromthe graph includes selecting at least one edge from the graph having aprobability greater than a confidence threshold;

wherein selecting a subsequent set of bridges from the graph includesselecting at least one subsequent edge from the graph that connects anode having no more than one outgoing edge to a node having no more thanone incoming edge; and

wherein selecting the at least one subsequent edge from the graphincludes selecting at least one subsequent edge from the graph having aprobability greater than a lower confidence threshold compared to theconfidence threshold.

X35. The method of Example X34, further comprising retrievingprobability information for the edges based on phenotypic information.

X36. The method of Example X35, wherein the phenotypic information isdetermined based on a population.

X37. The method of Example X35, wherein the local alignment is based onthe probability information.

X38. The method of Example X30, wherein the local alignment is based oninformation regarding the quality of the read.

X39. The method of Example X30, wherein the local alignment is based oninformation in a correlation table.

X40. The method of Example X39, wherein the information in thecorrelation table includes associations and co-occurrence scores for oneor more of genes, alleles, and mutations.

X41. The method of Example X34, further comprising updatingprobabilities in the graph based on information in a correlation table.

X42. The method of Example X30, further comprising updating informationwithin a correlation table based on the placement of the reads on thegraph.

X43. The method of Example X30, wherein the local alignment is performedusing a Smith-waterman algorithm, dynamic programming, orposition-specific scoring matrices.

X44. The method of Example X30, wherein using the score matrix todetermine a best combination of placements of reads for the set ofbridges includes performing an eigenvalue decomposition, a spectralmapping, or a functional analysis using Hilbert or Banach spaces.

X45. A system for generating graphs based on reference genomeinformation, the system comprising:

a graph data store configured to store a plurality of edge records,wherein each edge record includes a start node, an end node, a sequencelisting, and a probability value; and

at least one computing device configured to:

-   obtain mutation records representing polymorphisms within the    reference genome; and-   create and modify edge records within the graph data store based on    the mutation records.

X46. The system of Example X45, further comprising a correlation datastore configured to store a plurality of correlation records, whereineach correlation record indicates a probability of a second edge beingpresent given the presence of a first edge.

X47. The system of Example X45, wherein each edge record includes anindication of a population.

X48. The system of Example X45, wherein at least one edge recordincludes a start node and an end node that are the same.

X49. The system of Example X48, wherein the at least one edge recordthat includes a start node and an end node that are the same alsoincludes a value indicating a number of repetitions.

X50. A system for performing read alignments to a graph that representsa genome and polymorphisms therein, the system comprising:

a graph data store configured to store information representing thegraph, the information including a plurality of edge records;

at least one bridge computing device configured to:

-   receive a read pool;-   select a set of bridges from the edge records stored in the graph    data store;-   for each bridge in the set of bridges:    -   select a subset of the read pool, wherein reads in the subset        contain at least a portion of the bridge; and    -   transmit reads from the subset of the read pool and the bridge        to an alignment computing device;

a plurality of alignment computing devices each configured to:

-   receive one or more reads and a bridge with which the reads are    associated;-   perform a local alignment for each of the one or more reads;-   score the local alignment for each of the one or more reads to    generate a read-bridge pair score for each of the one or more reads;    and-   transmit the read-bridge pair scores to a matrix processing    computing device; and

at least one matrix processing computing device configured to:

-   receive read-bridge pair scores from the plurality of alignment    computing devices;-   insert the read-bridge pair scores into a score matrix;-   use the score matrix to determine a best combination of placements    of reads for the set of bridges; and-   place the reads on the graph.

X51. The system of Example X50, wherein selecting the set of bridgesfrom the graph includes selecting at least one edge from the graph thatconnects a node having no more than one outgoing edge to a node havingno more than one incoming edge.

X52. The system of Example X50, further comprising a correlation datastore configured to store a plurality of correlation records, whereineach correlation record indicates a probability of a second edge beingpresent given the presence of a first edge.

X53. The system of Example X52, wherein performing the local alignmentis based on the correlation records from the correlation data store.

X54. The system of Example X52, wherein placing the reads on the graphfurther includes updating information within the correlation data storebased on the placement of the reads on the graph.

X55. The system of Example X50, further comprising a computing deviceconfigured to present a personalization interface, wherein thepersonalization interface is configured to:

receive an indication of a phenotypic group; and

prune the graph to exclude edges from consideration for alignment thatare not likely to be found within the phenotypic group.

X56. The system of Example X50, wherein the graph includes a pluralityof edges, and wherein each edge includes sequence information.

X57. The system of Example X50, wherein the local alignment is performedusing a Smith-waterman algorithm, dynamic programming, orposition-specific scoring matrices.

X58. The method of Example X50, wherein using the score matrix todetermine a best combination of placements of reads for the set ofbridges includes performing an eigenvalue decomposition, a spectralmapping, or a functional analysis using Hilbert or Banach spaces.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A computer-implementedmethod of aligning reads of a read sequence to a graph that represents agenome and polymorphisms therein, wherein the graph includes a pluralityof edges, the method comprising: selecting a set of bridges from thegraph; for each bridge in the set of bridges: selecting a subset of aread pool, wherein reads in the subset contain at least a portion of thebridge; and for each read in the subset: performing a local alignmentfor the read; scoring the local alignment for the read to generate aread-bridge pair score; and inserting the read-bridge pair score into ascore matrix; using the score matrix to determine a best combination ofplacements of reads for the set of bridges; and placing the reads on thegraph.
 2. The method of claim 1, wherein selecting the set of bridgesfrom the graph includes selecting at least one edge from the graph thatconnects a node having no more than one outgoing edge to a node havingno more than one incoming edge.
 3. The method of claim 2, furthercomprising: pruning contradictory edges and superfluous edges from thegraph before selecting a subsequent set of bridges from the graph. 4.The method of claim 3, wherein selecting at least one edge from thegraph includes selecting at least one edge from the graph having aprobability greater than a confidence threshold; wherein selecting asubsequent set of bridges from the graph includes selecting at least onesubsequent edge from the graph that connects a node having no more thanone outgoing edge to a node having no more than one incoming edge; andwherein selecting the at least one subsequent edge from the graphincludes selecting at least one subsequent edge from the graph having aprobability greater than a lower confidence threshold compared to theconfidence threshold.
 5. The method of claim 4, further comprisingretrieving probability information for the edges based on phenotypicinformation, wherein the phenotypic information is determined based on apopulation.
 6. The method of claim 5, wherein the local alignment isbased on the probability information.
 7. The method of claim 1, whereinthe local alignment is based on information regarding the quality of theread.
 8. The method of claim 1, wherein the local alignment is based oninformation in a correlation table.
 9. The method of claim 8, whereinthe information in the correlation table includes associations andco-occurrence scores for one or more of genes, alleles, and mutations.10. The method of claim 1, further comprising updating informationwithin a correlation table based on the placement of the reads on thegraph.
 11. The method of claim 1, wherein the local alignment isperformed using a Smith-waterman algorithm, dynamic programming, orposition-specific scoring matrices.
 12. The method of claim 1, whereinusing the score matrix to determine a best combination of placements ofreads for the set of bridges includes performing an eigenvaluedecomposition, a spectral mapping, or a functional analysis usingHilbert or Banach spaces.
 13. A system for performing read alignments toa graph that represents a genome and polymorphisms therein, the systemcomprising: a graph data store configured to store informationrepresenting the graph, the information including a plurality of edgerecords; at least one bridge computing device configured to: receive aread pool; select a set of bridges from the edge records stored in thegraph data store; for each bridge in the set of bridges: select a subsetof the read pool, wherein reads in the subset contain at least a portionof the bridge; and transmit reads from the subset of the read pool andthe bridge to an alignment computing device; a plurality of alignmentcomputing devices each configured to: receive one or more reads and abridge with which the reads are associated; perform a local alignmentfor each of the one or more reads; score the local alignment for each ofthe one or more reads to generate a read-bridge pair score for each ofthe one or more reads; and transmit the read-bridge pair scores to amatrix processing computing device; and at least one matrix processingcomputing device configured to: receive read-bridge pair scores from theplurality of alignment computing devices; insert the read-bridge pairscores into a score matrix; use the score matrix to determine a bestcombination of placements of reads for the set of bridges; and place thereads on the graph.
 14. The system of claim 13, wherein selecting theset of bridges from the graph includes selecting at least one edge fromthe graph that connects a node having no more than one outgoing edge toa node having no more than one incoming edge.
 15. The system of claim13, further comprising a correlation data store configured to store aplurality of correlation records, wherein each correlation recordindicates a probability of a second edge being present given thepresence of a first edge.
 16. The system of claim 15, wherein performingthe local alignment is based on the correlation records from thecorrelation data store.
 17. The system of claim 15, wherein placing thereads on the graph further includes updating information within thecorrelation data store based on the placement of the reads on the graph.18. The system of claim 13, further comprising a computing deviceconfigured to present a personalization interface, wherein thepersonalization interface is configured to: receive an indication of aphenotypic group; and prune the graph to exclude edges fromconsideration for alignment that are not likely to be found within thephenotypic group.
 19. The system of claim 13, wherein the localalignment is performed using a Smith-waterman algorithm, dynamicprogramming, or position-specific scoring matrices.
 20. The method ofclaim 13, wherein using the score matrix to determine a best combinationof placements of reads for the set of bridges includes performing aneigenvalue decomposition, a spectral mapping, or a functional analysisusing Hilbert or Banach spaces.